Auroras come in a wide variety of colors — from green to pink to blue and purple — that can leave skywatchers both mesmerized and mystified. But there's a method to this auroral madness.
The alexandrite-like color change from blue-green in daylight to purple in incandescent light is mainly caused by relatively high amounts of vanadium (about 1 wt. % V 2 O 3). These garnets are ...